As a consequence of population growth, continued industrialization, and climate change, communities in developed and developing countries face dwindling water supplies and are turning to drinking water resources that have been impacted by agricultural runoff or wastewater discharges. Drinking water, surface water, and groundwater impaired by these anthropogenic activities contain pollutants including trace organic chemicals, known as organic micropollutants, such as pesticides, pharmaceuticals, components of personal care products, and other industrial chemicals. As these pollutants have gained attention and analytical techniques have improved, new emerging organic contaminants have been identified in water resources at a rapid pace. Toxicological data for these chemicals are limited, but significant developmental, reproductive, endocrine disrupting and other chronic health effects have been reported. Also, these pollutants can have negative effects on aquatic ecosystems, which serve as a basis of the food chain. Existing technologies for removing these emerging contaminants can be energy intensive, expensive, and are not always effective. Volatile organic compounds (VOCs) are a broad category of atmospheric contaminants emitted from industrial syntheses, transportation, and commercial products including solvent thinners, paint, cleaners, and lubricants. Several techniques have been applied to remove VOCs from air, most commonly through adsorption and sequestration.
Adsorption processes can be employed to remove specific contaminants or contaminant classes from fluids like air and water. Activated carbons (ACs) are the most widespread sorbents used to remove organic pollutants, and their efficacy derives primarily from their high surface areas, nanostructured pores, and hydrophobicity. However, no single type of AC removes all contaminants well. Because of their poorly defined structure and binding site variation, optimal adsorption selectivities require empirical screening at new installations, precluding rational design and improvement. Furthermore, regenerating spent AC is energy intensive (heating to 500-900° C. or other energy intensive procedures) and does not restore full performance. AC also has a slow pollutant uptake rate, achieving its uptake equilibrium in hours to days, such that more rapid contaminant removal requires excess sorbent. Finally, AC can perform poorly for many emerging contaminants, particularly those that are relatively hydrophilic.
An alternative adsorbent material can be made from polymeric cyclodextrin materials produced from insoluble polymers of β-cyclodextrin (β-CD), which are toroidal macrocycles comprised of seven glucose units whose internal cavities are capable of binding organic compounds. β-CD is an inexpensive and sustainably produced monomer derived from cornstarch that is used extensively to formulate and stabilize pharmaceuticals, flavorants, and fragrances, as well as within chiral chromatography stationary phases. Insoluble β-CD polymers have been formed by crosslinking with epichlorohydrin and other reactive compounds that feature well defined binding sites and high association constants. Insoluble βCD polymers crosslinked with epichlorohydrin have been investigated as alternatives to AC for water purification, but their low surface areas result in inferior sorbent performance relative to ACs.
Thus there is a need for new sorbents that address the deficiencies of AC and will provide more effective sorption and/or sequestration properties, for example in VOC adsorption or water purification applications, with reduced energy inputs. There is a need for an adsorbent that provides rapid contaminant extraction, high total uptake, and facile regeneration and reuse procedures. There is a need for a purification adsorbent that is inexpensive and can be reliably mass produced.